Machinery and equipment operated in harsh environments are often subject to accelerated corrosion rates which, if not monitored or controlled, can result in premature aging and eventually failure of the machinery and equipment. For example, in a gas turbine, high temperature combustion gases flow along a hot gas path through a turbine to produce work. The combustion gases may include sufficient quantities of oxygen to produce general corrosion on the metal surfaces along the hot gas path. The general corrosion is characterized by an oxidation-reduction reaction in which the metal surfaces are oxidized, producing an anode at the oxidation site and a cathode at the reduction site.
Sensors may be installed on the metal surfaces to monitor the presence and/or rate of any general corrosion. For example, as shown in FIG. 1, a conventional corrosion sensor 10 installed on a metal surface 12 may comprise alternating layers of electrodes 14 separated by dielectric material 16. The electrodes 14 may have an oxidation potential comparable to that of the metal surfaces 12 so that the general corrosion rate on the metal surfaces 12 may be approximated by the general corrosion rate on the electrodes 14. The general corrosion rate occurring on the metal surfaces 12 may thus be determined using a sensor 18 to measure the electrical potential or current flow across the electrodes 14.
The bond or interface between the electrodes 14 and the dielectric material 16 in the conventional corrosion sensor 10 may degrade over time, creating small gaps 19 or other low flow regions between the electrodes 14 and dielectric material 16, as shown in FIG. 1. These gaps 19 or low flow regions result in a local area conducive to crevice corrosion. Crevice corrosion between the electrodes 14 and dielectric material 16 exposes a larger surface area of the electrodes 14 to the hot gas path, increasing the electrical potential or current flow across the electrodes 14 for the same general corrosion rate. As a result, crevice corrosion changes the calibration and/or accuracy of the conventional corrosion sensors 10 over time. Therefore, a corrosion sensor and method for manufacturing a corrosion sensor resistive to crevice corrosion would be useful.